1. Field of the Invention
This invention relates to a process for the production of a biodegradable sheet formed of chitosan and cellulose.
In view of the recent increasing problems of environmental pollution, the use of biodegradable plastics which are able to be decomposed by microorganisms when left in soil is being encouraged.
Japanese Published Unexamined Patent Application (Tokkyo Kokai) No. Hei-2-6689 discloses a biodegradable composite sheet composed of cellulose and chitosan. Because of its excellent biodegradability and cheapness of its raw materials, this composite sheet will lend itself to a variety of applications for, for example, packaging and farm materials.
However, in order to actually put such a biodegradable sheet into practice, several problems have been found to remain unsolved. Thus, according to the method disclosed in the above Japanese patent publication, the composite sheet is produced by mixing an aqueous acidic solution of chitosan with fine cellulose fibers, shaping the resulting aqueous dispersion into a sheet and drying. Because the aqueous dispersion is viscous, air bubbles are apt to be trapped during the course of the preparation of the dispersion and the air bubbles once entrapped cannot be easily removed. Inclusion of air bubbles into the composite sheet causes deterioration of the mechanical properties, such as tensile strength, of the sheet.